Top Tips for Heating a Polytunnel in Winter

If you are feeling the chill, then it’s time to turn up the heat in your Polytunnel and keep young, tender plants snug and warm until spring arrives. Heating a polytunnel can be pricey but there is plenty that you can do to keep costs down.

Keep Your Crops Warm

We know heating a Polytunnel or Greenhouse can be an expensive luxury and nobody likes the idea of wasting energy or money, so here are some top tips to help keep costs down and make heating your Polytunnel more efficient this winter.

1) Insulate with bubble wrap

A layer of bubble wrap fastened with string inside your Polytunnel will help to block icy draughts and reduce heat loss. Simply tie a string between the hoops and carefully – although a little bit fiddly, feed the bubble wrap between the polythene cover and the string..When buying bubble wrap, look for the purpose made horticultural bubble wrap insulation as it is toughened and UV stabilised.

Larger bubbles will let more light in. You can also use bubble wrap insulation to protect outdoor pots preventing your favourite pots from cracking in freezing weather.

2) Only heat the area that you need to

Heating a large Polytunnel or Greenhouse can be wasteful and expensive especially if you only have a few delicate plants you wish to nurture throughout the winter months. Try to group them together in one section, create a bubble wrap insulation curtain to divide the Polytunnel into smaller areas which can be heated more economically. Using a mini Polytunnel inside a Polytunnel like “double glazing” along with a few candles will help raise the temperature.

3) Use horticultural fleece

It can be a good idea to have something like horticultural fleece on hand to drape over your crops when a hard frost is forecast. With hardy plants such as kale or winter cabbages, simply laying the fleece over the plants in question should be fine.

For delicate salad crops, however, it may be better to use the horticultural fleece in conjunction with a tenting or framing structure, to keep the fabric weight off the plants. Garden canes or small branches can be used to create a simple tent, or you can create a tunnel within your polytunnel be using lengths of plastic piping to make arches to hold the fleece off the plants.

Horticultural fleece can also be used to great effect to protect tender fruiting trees from the worst of the cold. In these cases, the fleece can simply be draped over the branches.

Horticultural fleece is not the only option. If you are looking for a more eco-friendly alternative to keep plants warm in winter, you could also consider using old sheets, or other scrap material to add an extra layer of protection between your plants and the cold outside air.

4) Protect plant roots with an organic mulch

You can also help to protect plant roots from frost by mulching with a thick layer of straw, leaves or other organic matter. Mulching will not only add a little extra protection and reduce heating needs, it will also add fertility to the soil ready for spring sowing and planting.

5) Add Thermal Mass To Your Polytunnel

Another way to reduce heating needs in your polytunnel is to add thermal mass in the form of stone, clay, brick or tile, which will store heat during the day and release it gradually during the night, helping to keep off the chill. You could also add water containers inside your polytunnel, as these too will be excellent at storing heat and releasing it later. You can add thermal mass on your polytunnel paths, bed edges or as part of your staging set up.

6) Create a Hot Bed With Straw/ Compost

If you have particular plants that need to remain warmer over winter, you could consider growing these in a hot bed, made with decomposing straw and other organic material. As the straw/ manure/ compost and other materials decompose, heat will be given off, and this area can be much warmer than the rest of your polytunnel.

7) Create Cloches with Plastic Waste

If you have individual tender plants and seedlings, you can protect these from the cold by using cloches or mini polytunnels. You can make your own small cloches simply and cheaply using plastic drinks bottles cut in half and placed over these plants.

These are just some of the ways to cut down on the cost of heating a polytunnel in winter. Read our other guides to discover interesting and eco-friendly ways to heat the space.